JP2022039962A - Positive electrode active material and lithium secondary battery comprising the same - Google Patents

Abstract

To provide a lithium secondary battery which prevents decrease in electrochemical characteristics and stability of a positive electrode active material caused by Li impurities remaining on a surface of the positive electrode active material.SOLUTION: A positive electrode active material comprises: a first compound enabling lithium intercalation/deintercalation; and a coating layer present on at least a part of a surface of the first compound, and comprising a second compound, where the second compound is an oxide comprising at least one first element selected from Group 1A elements, Group 3A elements and Group 5A elements and also comprising at least one second element selected from Group 8 elements.SELECTED DRAWING: None

Description

The present invention relates to a positive electrode active material having improved electrochemical characteristics and stability and a lithium secondary battery using a positive electrode containing the positive electrode active material. More specifically, the present invention relates to the surface of the positive electrode active material. In order to reduce the amount of residual lithium present in the surface, the content of Li impurities remaining on the surface is controlled without going through a washing step to control the electrochemical properties and stability of the positive electrode active material due to the Li impurities. The present invention relates to a positive electrode active material capable of preventing a decrease in advance and a lithium secondary battery using a positive electrode containing the positive electrode active material.

A battery stores electric power by using a substance capable of an electrochemical reaction between a positive electrode and a negative electrode. A typical example of such a battery is a lithium secondary battery that stores electrical energy by the difference in chemical potential when lithium ions are intercalated / deintercalated at the positive and negative electrodes. There is.

The lithium secondary battery uses a substance capable of reversible intercalation / deintercalation of lithium ions as a positive electrode and a negative electrode active material, and an organic electrolytic solution or a polymer electrolytic solution is used between the positive electrode and the negative electrode. Is filled and manufactured.

Lithium composite oxides are used as the positive electrode active material of the lithium secondary battery, and composite oxides such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiMnO ₂ have been studied as examples.

Among the positive electrode active materials, LiCoO ₂ has excellent life characteristics and charge / discharge efficiency, and is most often used. However, it is expensive due to the resource limit of cobalt used as a raw material, so that its price competitiveness is limited. It has the disadvantage of.

Lithium manganese oxides such as LiMnO ₂ and LiMn _{2O 4} have advantages of excellent thermal safety and low price, but have problems of small capacity and poor high temperature characteristics. In addition, the LiNiO ₂ -based positive electrode active material exhibits high discharge capacity battery characteristics, but is difficult to synthesize due to the problem of cation mixing between Li and the transition metal, which causes the rate ( rate) There is a big problem with the characteristics.

In addition, a large amount of Li by-products are generated depending on the degree of deepening of such cation mixing, and most of these Li by-products are composed of compounds of LiOH and Li ₂ CO ₃ , so that a gel is produced during the production of the positive electrode paste. It causes the problem of becoming (gel) and gas generation due to the progress of charging and discharging after the electrode is manufactured. Residual Li ₂ CO ₃ increases the swelling phenomenon of the cell, reduces the cycle and causes the battery to swell.

On the other hand, the content of Li impurities present on the surface of the positive electrode active material tends to increase proportionally with the content of Ni in the positive electrode active material.

As a result, in the case of the high-Ni type positive electrode active material recently introduced to improve the capacity characteristics of the positive electrode active material, an excessive amount of Li impurities in the surface is present, and a washing step for removing the Li impurities is performed. It can be said that it is indispensable.

However, although the residual lithium present on the surface of the positive electrode active material can be reduced through such a washing step, there is a disadvantage that the surface of the positive electrode active material can be damaged. If the surface of the positive electrode active material is damaged through the washing step, the electrochemical properties and stability of the positive electrode active material may deteriorate.

Korean Patent Publication No. 10-2016-0112622

It is an object of the present invention to provide a positive electrode active material having improved electrochemical characteristics and stability in order to solve various problems of the positive electrode active material for a lithium secondary battery. In particular, in the present invention, in order to reduce the amount of residual lithium present on the surface of the positive electrode active material, the content of Li impurities remaining on the surface is controlled without going through a washing step, and the positive electrode caused by the Li impurities is controlled. It is an object of the present invention to provide a positive electrode active material capable of preventing deterioration of the electrochemical properties and stability of the active material in advance.

Another object of the present invention is to provide a positive electrode containing the positive electrode active material defined in the present application.

Yet another object of the present invention is to provide a lithium secondary battery using the positive electrode defined in the present application.

The object of the present invention is not limited to the object mentioned above, and other purposes and advantages of the present invention not mentioned may be understood by the following description and more clearly understood by the examples of the present invention. .. In addition, it can be easily known that the object and the advantage of the present invention can be realized by the means and combinations thereof shown in the claims.

According to one aspect of the present invention, a first compound capable of intercalating / deintercalating lithium and a coating layer present on at least a part of the surface of the first compound and containing the second compound. A positive electrode active material containing, is provided.

At this time, the second compound is an oxide containing at least one first element selected from Group 1A elements, Group 3A elements and Group 5A elements, and at least one second element selected from Group 8 elements. It is possible.

Here, the first compound can be represented by the following chemical formula 1.
[Chemical formula 1]
Li _w Ni _{1- (x + y + z)} Co _x M1 _y M2 _z O _{2 + α}
(here,
M1 is at least one selected from Mn or Al, and is
M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu. ,
M1 and M2 are different elements from each other,
0.5 ≦ w ≦ 1.5, 0 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.20, 0 ≦ z ≦ 0.20, 0 ≦ α ≦ 0.02. )

The second compound can be represented by the following chemical formula 2.
[Chemical formula 2]
Li _a Co _b M3 _c (P _β O _γ ) _d
(here,
M3 is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ a ≦ 10, 0 ≦ b ≦ 8, 0 ≦ c ≦ 8, 0 <d ≦ 13, 0 <β ≦ 4, 0 <γ ≦ 10. )

At this time, the second compound can include a first oxide represented by the following chemical formula 3 and a second oxide represented by the following chemical formula 4.
[Chemical formula 3]
Li _{a'Co b'M3'c' ( P β'O γ'} ) _d'
(here,
M3'is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 <a'≤10, 0≤b'≤8, 0≤c'≤8, 0 <d'≤13, 0≤β'≤4, 0 <γ'≤10. )
[Chemical formula 4]
Co _{b ″} M3 ″ _{c ″} (P _{β ″} O _{γ ″} ) _{d ″}
(here,
M3 ″ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ b ″ ≦ 8, 0 ≦ c ″ ≦ 8, 0 <d ″ ≦ 13, 0 ≦ β ″ ≦ 4, 0 <γ ″ ≦ 10)

In another embodiment, at least a part of the surface of the first compound may further contain the third compound represented by the following chemical formula 5.
[Chemical formula 5]
Li _e W _f M4 _{g Oh}
(here,
M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ e ≦ 10, 0 <f ≦ 8, 0 ≦ g ≦ 8, 2 ≦ h ≦ 13. )

Further, according to another aspect of the present invention, a positive electrode containing the above-mentioned positive electrode active material is provided.

Further, according to still another aspect of the present invention, there is provided a lithium secondary battery using the above-mentioned positive electrode.

The positive electrode active material according to the various embodiments of the present invention comprises an in-surface lithium metal oxide and / or lithium metal phosphate without a washing step to reduce the amount of residual lithium present on the surface of the positive electrode active material. It is possible to form and control the content of Li impurities remaining on the surface.

This makes it possible to prevent deterioration of the electrochemical properties and stability of the positive electrode active material due to the Li impurities remaining on the surface of the positive electrode active material in advance.

Through this, the lithium secondary battery uses the positive electrode active material according to various embodiments of the present invention, and is an important index for evaluating the performance of the lithium secondary battery, such as capacity characteristics, life characteristics, rate characteristics, etc. Various electrochemical properties such as can be improved.

Along with the above-mentioned effects, the specific effects of the present invention will be described together while explaining specific matters for carrying out the invention below.

For convenience, specific terms are defined herein in order to better understand the invention. Unless otherwise defined herein, the scientific and technical terms used in the present invention have the meaning generally understood by those with ordinary knowledge in the art. Also, in context, unless otherwise specified, a singular term shall be understood to include its plural form, and a plural form term shall be understood to include its singular form as well.

Hereinafter, the positive electrode active material according to the present invention, the positive electrode containing the positive electrode active material, and the lithium secondary battery using the positive electrode will be described in more detail.

Positive Electrode Active Material According to one aspect of the present invention, it comprises a first compound capable of intercalating / deintercalating lithium and a coating layer present on at least a part of the surface of the first compound. Positive electrode active material is provided.

The first compound may be a single crystal or polycrystalline lithium composite oxide, but is preferably a polycrystalline lithium composite oxide. The polycrystalline-form lithium composite oxide means an agglomerate containing primary particles and secondary particles in which the primary particles are aggregated in a plurality.

The primary particles mean a single crystal grain (grain or crystallite), and the secondary particles mean an agglomerate formed by aggregating a plurality of primary particles. Voids and / or grain boundaries can be present between the primary particles constituting the secondary particles.

For example, the primary particles can form internal voids inside the secondary particles separated from adjacent primary particles. Further, the primary particles do not contact each other with adjacent primary particles to form crystal grain boundaries, but can form a surface existing inside the secondary particles by contacting with internal voids.

On the other hand, the surface of the secondary particles on the outermost surface where the primary particles are exposed to the outside air forms the surface of the secondary particles.

Here, the average particle size of the primary particles is in the range of 0.1 μm to 5 μm, preferably 0.1 μm to 3 μm, and thus the positive electrode active material according to various examples of the present invention is used. The optimum density of the manufactured positive electrode can be realized. The average particle size of the secondary particles can vary from 3 μm to 20 μm, depending on the number of aggregated primary particles.

Further, the primary particles and / or the secondary particles can have a rod shape, an elliptical shape and / or an amorphous shape.

Here, the first compound is a lithium composite oxide represented by the following chemical formula 1.
[Chemical formula 1]
Li _w Ni _{1- (x + y + z)} Co _x M1 _y M2 _z O _{2 + α}
(here,
M1 is at least one selected from Mn or Al, and is
M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu. ,
M1 and M2 are different elements from each other,
0.5 ≦ w ≦ 1.5, 0 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.20, 0 ≦ z ≦ 0.20, 0 ≦ α ≦ 0.02. )

At this time, the first compound may be a lithium composite oxide having a layered crystal structure containing at least Ni and Co. Further, the first compound is preferably a high—Ni type lithium composite oxide having x + y + z of 0.20 or less in the chemical formula 1.

As described above, in the case of a lithium composite oxide containing Ni, a large amount of residual lithium, that is, a Li impurity may be formed on the surface of the lithium composite oxide as the cation mixing of Li and Ni becomes more intense. The Li impurities mainly contain LiOH and Li ₂ CO ₃ , and the Li impurities cause gelation during the production of a paste for producing a positive electrode or cause a cell swelling phenomenon.

The content of the Li impurity increases proportionally as the content of Ni in the lithium composite oxide increases, but in general, the content of Ni is 80 mol% or more, which is a high-Ni type positive electrode active material (lithium). In the case of composite oxides), a washing step to remove Li impurities on the surface must be essential. However, the washing step can rather partially cause surface damage to the lithium composite oxide, which may act as a cause of deteriorating the electrochemical properties and stability of the lithium composite oxide. can.

On the other hand, the lithium composite oxide according to various examples of the present invention and the positive electrode active material containing the lithium composite oxide form a lithium metal oxide and / or a lithium metal phosphate described later in the lithium composite oxide. Thereby, it is possible to effectively reduce the content of Li impurities remaining on the surface of the lithium composite oxide without a washing step.

Further, the first compound can be doped with a metal element represented by M1 as shown in the chemical formula 1, and preferably M1 can contain tungsten (W).

At this time, the tungsten can be present in the crystal lattice of the first compound. That is, the tungsten can be present in the first compound in a state of being replaced with Ni inserted into at least one of the Li 3a site and the 3b site.

On the other hand, when the tungsten is doped with the first compound, the proportion of Ni inserted into the Li 3a site by _Rietveld analysis of the X-ray diffraction pattern can be improved, and through this, the positive electrode active material can be improved. The electrochemical properties and stability of the above can be improved. At this time, the ratio Ni _occ of Ni inserted into the Li 3a site may be associated with an increase in the amount of Ni inserted into the Li 3a site due to the doping of the tungsten, but the Li 3a site. It can also be increased as W is inserted into. Preferably, when the tungsten is doped with the first compound, the electrochemical properties of the first compound as at least a part of the tungsten doped with the first compound is inserted into the Li 3a site. And can contribute to the improvement of stability and the like.

In this case, the first compound can be represented by the following chemical formula 1-1.
[Chemical formula 1-1]
Li _w Ni _{1- (x + y + z)} Co _x M1 _y M2 _z W _{z'O 2 + δ}
(here,
M1 is at least one selected from Mn or Al, and is
M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb and Cu.
M1 and M2 are different elements from each other,
0.5 ≦ w ≦ 1.5, 0 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.20, 0 ≦ z ≦ 0.20, 0 ≦ z ′ ≦ 0.20, 0 ≦ δ ≦ 0.02 Is. )

In addition, M1 present in the lithium composite oxide can exhibit a concentration gradient that decreases from the surface portion to the central portion of the secondary particles.

The concentration gradient has a (-) gradient between the concentration of M1 at an arbitrary point on the surface of the secondary particle and the concentration of M1 at an arbitrary point on the center of the secondary particle. Means that.

As described above, as the concentration gradient of M1, preferably tungsten (W) is present in the secondary particles, the movement path of the secondary particles and the lithium ions in the primary particles constituting the secondary particles (as described above). The diffusion path of lithium ions) can be formed in the direction from the surface portion to the center portion of the secondary particles.

The positive electrode active material according to various examples of the present invention is characterized in that a coating layer containing the second compound is provided on the surface in order to reduce the content of residual Li, that is, a Li impurity present on the surface of the first compound. And.

At this time, the second compound can be present at least on the interface between the primary particles of the first compound and the surface of the secondary particles formed by the aggregation of the primary particles. Further, the concentration of the second compound can show a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles.

The coating layer is an oxide containing at least one first element selected from Group 1A elements, Group 3A elements and Group 5A elements, and at least one second element selected from Group 8 elements. Can include compounds.

The second compound can be represented by the following chemical formula 2.
[Chemical formula 2]
Li _a Co _b M2 _c (P _β O _γ ) _d
(here,
M2 is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ a ≦ 10, 0 ≦ b ≦ 8, 0 ≦ c ≦ 8, 0 <d ≦ 13, 0 <β ≦ 4, 0 <γ ≦ 10. )

At this time, the second compound may be a single crystalline structure or an amorphous oxide, but is not necessarily limited to this, and is not limited to this, and is not limited to this, and is an oxide having at least one crystalline structure and / or an amorphous heterogeneous oxide. Can be a set of.

If at least one of the second compounds is an oxide having a crystal structure, the second compound has a crystal structure belonging to the space group Fd-3m, Pnma, P * / n, R3c or R-3m. Can have. At this time, the crystal structure may be a monoclinic, cubic, orthorhombic or rhombohedron crystal structure.

In a preferred case, the proportion of the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the second compound in order to effectively remove the residual Li existing on the surface of the first compound. Is preferably 13 mol% or less, more preferably 10 mol% or less, and more preferably 5 mol% or less. In the second compound, the crystal structure belonging to the space group Fd-3m, R3c or R-3m can be a cubic or rhombohedral crystal structure.

Among the second compounds, typical examples of oxides having a crystal structure belonging to the space group Fd-3m, R3c or R-3m include Co ₃ O ₄ , LiCo O ₂ and P ₂ O ₅ , and others. Further, by being present on the surface of the first compound, an oxide that can act as an impurity similar to residual Li as it is present on the surface of the first compound can be further contained.

In order to effectively remove the residual Li existing on the surface of the first compound, the ratio of the compound having a crystal structure belonging to the space group Fd-3m, R3c or R-3m in the second compound is 13 mol%. If the above amount is exceeded, the effect of the second compound on improving the electrochemical properties and stability of the positive electrode active material may be small, or rather the electrochemical properties and stability of the positive electrode active material may be deteriorated. There is.

Further, the second compound can include a first oxide represented by the following chemical formula 3 and a second oxide represented by the following chemical formula 4.
[Chemical formula 3]
Li _{a'Co b'M3'c' ( P β'O γ'} ) _d'
(here,
M3'is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 <a'≤10, 0≤b'≤8, 0≤c'≤8, 0 <d'≤13, 0≤β'≤4, 0 <γ'≤10. )
[Chemical formula 4]
Co _{b ″} M3 ″ _{c ″} (P _{β ″} O _{γ ″} ) _{d ″}
(here,
M3 ″ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ b ″ ≦ 8, 0 ≦ c ″ ≦ 8, 0 <d ″ ≦ 13, 0 ≦ β ″ ≦ 4, 0 <γ ″ ≦ 10)

For example, the first oxide may be lithium phosphate, lithium cobalt phosphate, lithium metal (cobalt excluded) phosphate, lithium metal (cobalt excluded) -cobalt phosphate, lithium cobalt oxide and / or lithium metal (cobalt excluded) oxide. The second oxide may be phosphorus pentoxide, cobalt phosphate, metal (cobalt excluded) phosphate, metal (cobalt excluded) -cobalt phosphate, cobalt oxide and / or metal (cobalt excluded) oxide.

In addition, the ratio of the first oxide and the second oxide (first oxide / second oxide) as defined above in the second compound present in the coating layer is 0. It is preferably 87 or more.

When the ratio of the first oxide and the second oxide (first oxide / second oxide) in the second compound existing in the coating layer is less than 0.87 (that is, lithium phosphate). (When the ratio of the metal oxide to the salt is large), the effect of the second compound on improving the electrochemical characteristics and stability of the positive electrode active material is small, or rather, the electrolytic chemistry of the positive electrode active material. There is a risk of degrading the target characteristics and stability.

Further, as described above, the first oxide and the second oxide can exhibit a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. The Co concentration in the lithium composite oxide can also show a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles.

In another embodiment, at least a part of the surface of the first compound may further contain the third compound represented by the following chemical formula 5.
[Chemical formula 5]
Li _e W _f M4 _{g Oh}
(here,
M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ e ≦ 10, 0 <f ≦ 8, 0 ≦ g ≦ 8, 2 ≦ h ≦ 13. )

The third compound may exist in the coating layer in which the second compound is present, or may exist independently of the coating layer. Further, the third compound can be present at least on the interface between the primary particles of the first compound and the surface of the secondary particles formed by the aggregation of the primary particles. Further, the concentration of the third compound can show a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles.

In yet another embodiment, the positive electrode active material further comprises a shell layer that covers at least a portion of the surface of the first compound (the surface not covered by the coating layer) and the surface of the coating layer. Can be done.

At this time, the shell layer can contain a fourth compound represented by the following chemical formula 4. That is, the shell layer can be defined as a region in which the fourth compound represented by the following chemical formula 4 is present.
[Chemical formula 4]
Li _j M4 _k O _l
(Here, M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm. , W, Ce, V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ j ≦ 10, 0 ≦ k ≦ 8, 2 ≦ l ≦ 13. )

Further, the shell layer may be in a form in which a different kind of fourth compound in one layer is present at the same time, or a different kind of fourth compound represented by the chemical formula 4 is present in separate layers.

The fourth compound represented by the chemical formula 4 may be in a state of being physically and / or chemically bonded to the first compound, the second compound and / or the third compound. Further, the fourth compound may exist in a state of forming a solid solution with the first compound, the second compound and / or the third compound.

The fourth compound is an oxide in which lithium and an element represented by M4 are combined, or as an oxide of M4, the oxide is, for example, Li _a W _b O _c , Li _a Zr _b O. _c , Li _a Ti _b O _c , Li _a Ni _b O _c , Li _a B _b O _c , W _b O _c , Zr _b O _c , Ti _b O _c , B _b O _c , etc., as described above. The examples are provided for convenience only to aid understanding, and the oxides defined in the present application are not limited to the above-mentioned examples.

In another embodiment, the fourth compound is an oxide in which at least two elements represented by lithium and M4 are compounded, or at least two elements represented by lithium and A are compounded. It can further contain the oxides that have been formed. Oxides in which at least two elements represented by lithium and M4 are combined are, for example, Li _a (W / Ti) _b O _c , Li _a (W / Zr) _b O _c , Li _a (W / Ti). / Zr) _b O _c , Li _a (W / Ti / B) _b O _c , etc., but are not necessarily limited to this.

Here, the fourth compound can show a concentration gradient that decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. Thereby, the concentration of the fourth compound can be reduced from the outermost surface of the secondary particles toward the center of the secondary particles.

As described above, residual Li present on the surface of the first compound is added by showing a concentration gradient in which the fourth compound decreases from the surface portion of the secondary particles toward the center portion of the secondary particles. Can be reduced. Further, it is possible to prevent the crystallinity of the first compound from being lowered in the surface inner region by the fourth compound. In addition, it is possible to prevent the fourth compound from disrupting the overall structure of the positive electrode active material during the electrochemical reaction.

In addition, the shell layer comprises a first shell layer containing at least one fourth compound represented by the chemical formula 4 and at least one fourth compound represented by the chemical formula 4 and the first shell. A second shell layer containing an oxide different from the oxide contained in the layer can be included.

Lithium Secondary Battery According to still another aspect of the present invention, a positive electrode including a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector can be provided. Here, the positive electrode active material layer can contain the positive electrode active material according to various examples of the present invention. Therefore, since the positive electrode active material is the same as that described above, a specific description thereof will be omitted for convenience, and only the remaining configurations not described above will be described below.

The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and is not particularly limited, for example, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum or stainless steel. A steel surface treated with carbon, nickel, titanium, silver or the like can be used. Further, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

The positive electrode active material layer can be produced by applying a positive electrode slurry composition containing a conductive material and, if necessary, a binder, together with the positive electrode active material, to the positive electrode current collector.

At this time, the positive electrode active material may be contained in a content of 80 to 99 wt%, more specifically, 85 to 98.5 wt% with respect to the total weight of the positive electrode active material layer. When contained in the above content range, it can exhibit excellent volumetric properties, but is not necessarily limited to this.

The conductive material is used to impart conductivity to the electrodes, and can be used without any special limitation as long as it does not cause a chemical change and has electronic conductivity in the constituent battery. It is possible. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; copper, nickel, and the like. Examples thereof include metal powders or metal fibers such as aluminum and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One type alone or a mixture of two or more types may be used. The conductive material may be contained in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacryllonerile, carboxymethyl cellulose (CMC), starch, and hydroxypropyl. Cellulose, regenerated cellulose, polyvinylpyrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. However, one of these may be used alone or a mixture of two or more thereof may be used. The binder may be contained in an amount of 0.1 to 15 wt% based on the total weight of the positive electrode active material layer.

The positive electrode can be manufactured by a usual method for manufacturing a positive electrode, except that the positive electrode active material described above is used. Specifically, the positive electrode active material described above and, optionally, a positive electrode slurry composition produced by dissolving or dispersing a binder and a conductive material in a solvent are applied onto a positive electrode current collector, and then dried and rolled. Can be manufactured.

The solvent may be a solvent generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol (isopropanol alcohol), N-methylpyrrolidone (NMP), and acetone (acetone). Alternatively, water or the like may be mentioned, and one of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is such that the positive electrode active material, the conductive material and the binder are dissolved or dispersed in consideration of the coating thickness of the slurry and the production yield, and thereafter, excellent thickness uniformity is obtained at the time of coating for the production of the positive electrode. It is sufficient to have a viscosity that can be shown.

Further, in another embodiment, the positive electrode is formed by casting the positive electrode slurry composition onto another support and then laminating a film obtained by peeling from the support onto a positive electrode current collector. It can also be manufactured.

Further, according to still another aspect of the present invention, an electrochemical device including the above-mentioned positive electrode can be provided. The electrochemical element may be specifically a battery, a capacitor or the like, and more specifically, a lithium secondary battery.

Specifically, the lithium secondary battery can include a positive electrode, a negative electrode located facing the positive electrode, and a separation membrane and an electrolyte interposed between the positive electrode and the negative electrode. Here, since the positive electrode is the same as that described above, a specific description thereof will be omitted for convenience, and only the remaining configurations not described above will be specifically described below.

The lithium secondary battery can optionally further include a battery container for accommodating the positive electrode, the negative electrode and the electrode assembly of the separation membrane, and a sealing member for sealing the battery container.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity, and is not particularly limited, for example, copper, stainless steel, aluminum, nickel, titanium, and fired. A surface-treated carbon, copper, stainless steel surface with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, or the like can be used. Further, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities are formed on the surface of the current collector to bond the negative electrode active material. Can also be strengthened. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

The negative electrode active material layer can be produced by applying a negative electrode slurry composition containing a conductive material and, if necessary, a binder, together with the negative electrode active material, to the negative electrode current collector.

As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, and Si alloys. Metallic compounds capable of alloying with lithium, such as Sn alloys or Al alloys; can be doped and dedoped with lithium such as SiO _β (0 <β <2), SnO ₂ , vanadium oxide, lithium vanadium oxide. Metal oxides; or composites containing the metallic compound and a carbonaceous material, such as a Si—C complex or a Sn—C complex, and a mixture of any one or more of these. Can be used. Further, a metallic lithium thin film can also be used as the negative electrode active material. Further, as the carbon material, low crystalline carbon, high crystalline carbon and the like can all be used. Typical examples of low crystalline carbon are soft carbon and hard carbon, and examples of high crystalline carbon are amorphous, plate-like, scaly, spherical or fibrous natural graphite. Or artificial graphite, Kish graphite, thermally decomposed carbon (pyrolic carbon), liquid crystal pitch carbon fiber (mesophase platinum based carbon fiber), carbon microspheres (meso-carbon microbeads), liquid crystal pitch (meso-carbon microbeads), liquid crystal pitch. And high-temperature calcined carbon such as petroleum or coal tar pitch divided cokes are typical.

The negative electrode active material may be contained in an amount of 80 to 99 wt% based on the total weight of the negative electrode active material layer.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can be usually added in an amount of 0.1 to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders are polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-. Examples thereof include diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, graphite such as natural graphite or artificial graphite; acetylene black, etc. Carbon black such as kechen black, channel black, furnace black, lamp black, thermal black; conductive fiber such as carbon fiber and metal fiber; metal powder such as carbon fluoride, aluminum and nickel powder; zinc oxide, potassium titanate Such as conductive whisker; conductive metal oxide such as titanium oxide; conductive material such as polyphenylene derivative and the like can be used.

In one embodiment, the negative electrode active material layer is dried by applying a negative electrode active material and a negative electrode slurry composition produced by selectively dissolving or dispersing a binder and a conductive material in a solvent on the negative electrode current collector. This can be produced by casting the negative electrode slurry composition onto another support, and then laminating the film obtained by peeling from the support onto the negative electrode current collector.

On the other hand, in the lithium secondary battery, the separation film separates the negative electrode and the positive electrode to provide a movement passage for lithium ions, and is usually used as a separation film in the lithium secondary battery. It can be used without any special limitation, and it is particularly preferable that the resistance to ion transfer of the electrolyte is low and the electrolyte impregnation ability is excellent. Specifically, porous polymer films such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers and the like are polyolefin-based polymers. A porous polymer film produced in 1 or a laminated structure having two or more layers thereof can be used. Further, a normal porous non-woven fabric, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like can also be used. Further, a coated separation membrane containing a ceramic component or a polymer substance can be used for ensuring heat resistance or mechanical strength, and may be selectively used in a single layer or a multilayer structure.

The electrolyte used in the present invention includes an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-like polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte that can be used in the manufacture of a lithium secondary battery. Examples thereof include, but are not limited to, electrolytes.

Specifically, the electrolyte can include an organic solvent and a lithium salt.

The organic solvent can be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; dibutyl ether ( Ether-based solvent such as dibutyl ether) or tetrahydrofuran (tellahydrofuran); Ketone-based solvent such as cyclohexanone; Aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; dimethyl carbonate, dimethylcarbon , Dithylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (ethylene carbonone, EC), propylene carbonate (propylene solvent; Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; R-CN (R is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and has a double-bonded aromatic ring or ether bond. Nitriles such as (which can be included); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or solvents and the like can be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates having high ionic conductivity and high dielectric constant (for example, ethylene carbonate or propylene carbonate) that can enhance the charge / discharge performance of the battery and low-viscosity linear carbonates. Mixtures of system compounds (eg, ethylmethyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred. In this case, the performance of the electrolytic solution can be excellently exhibited by mixing the cyclic carbonate and the chain carbonate in a volume ratio of about 1: 1 to about 1: 9.

The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salts are LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (C ₂ F ₅ SO ₃ ). ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiCl, LiI, or LiB (C ₂ O ₄ ) ₂ and the like can be used. The concentration of the lithium salt is preferably used in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited and lithium ions can be effectively transferred.

In addition to the electrolyte constituent components, the electrolyte is a haloalkylene carbonate type such as difluoroethylene carbonate for the purpose of improving the life characteristics of the battery, suppressing the decrease in the battery capacity, improving the discharge capacity of the battery, and the like. Compound, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene. One or more additives such as glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further contained. At this time, the additive may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

As described above, the lithium secondary battery containing the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics. It is also useful in the field of electric vehicles such as hybrid electric vehicles (HEV).

The outer shape of the lithium secondary battery according to the present invention is not particularly limited, but may be a cylinder, a square, a pouch, a coin, or the like using a can. In addition, the lithium secondary battery can be used as a battery cell used as a power source for a small device, and can also be preferably used as a unit battery in a medium-sized battery module including a large number of battery cells.

According to still another aspect of the present invention, a battery module containing the lithium secondary battery as a unit cell and / or a battery pack containing the same can be provided.

The battery module or the battery pack is a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (Plug-in Hybrid Electric Vehicle, PHEV); Alternatively, it is used as a power source for a medium-sized or large device of any one or more of the power storage systems.

Hereinafter, the present invention will be described in more detail through examples. However, it can be said that these examples are merely for exemplifying the present invention, and it cannot be understood that the scope of the present invention is limited by these examples.

Experimental example 1.
Production example 1. Production of Positive Electrode Active Material (1) Example 1
A spherical Ni _0.91 Co _0.08 Mn _0.01 (OH) ₂ hydroxide precursor was synthesized by the co-precipitation method. Specifically, 25 wt% NaOH and 30 wt% NH ₄ are mixed in a 1.5 M composite transition metal sulfuric acid aqueous solution in which nickel sulfate, cobalt sulfate and manganese sulfate are mixed in a molar ratio of 91: 8: 1 in a 90 L class reactor. OH was added. The pH in the reactor is maintained at 11.5, the temperature of the reactor is maintained at 60 ° C., and the inert gas N ₂ is charged into the reactor so that the produced precursor does not oxidize. I did it. After completion of the synthetic agitation, washing and dehydration were carried out using a Filter press (F / P) equipment to obtain a Ni _0.91 Co _0.08 Mn _0.01 (OH) ₂ hydroxide precursor.

Next, LiOH (Li / (Ni + Co + Mn) mol ratio = 1.01) was mixed with the synthesized precursor, and then the temperature was raised to 700 ° C. at 2 ° C. per minute while maintaining the _O2 atmosphere in the firing furnace. And heat-treated for 10 hours to obtain a lithium composite oxide.

Next, the lithium composite oxide, a Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and a W-containing raw material (WO ₃ ) were mixed and then fired to finally produce a positive electrode active material. Specifically, after mixing the lithium composite oxide with the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ), the temperature is 400 ° C. while maintaining the O ₂ atmosphere in the firing furnace. The temperature was raised to 2 ° C. per minute, heat-treated for 5 hours, and then naturally cooled to obtain a positive electrode active material.

The Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ) are the lithium composite oxide, the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material, respectively. It was mixed so as to be 0.3 mol% with respect to the mixture of (WO ₃ ).

The ICP analysis results for the composition of the positive electrode active material are shown in Table 1 below.

(2) Example 2
The Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) is added to the mixture of the lithium composite oxide, the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ). The positive electrode active material was produced in the same manner as in Example 1 except that the mixture was mixed so as to be 5 mol%. The ICP analysis results for the composition of the positive electrode active material are shown in Table 2 below.

(3) Example 3
The W-containing raw material (WO ₃ ) is adjusted to 1.0 mol% with respect to the mixture of the lithium composite oxide, the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ). The positive electrode active material was produced in the same manner as in Example 1 except that it was mixed with. The ICP analysis results for the composition of the positive electrode active material are shown in Table 3 below.

（４）実施例４
合成された前駆体にＺｒ含有化合物（ＺｒＯ_２）０．０５モル％を追加的に混合したことを除いて、実施例１と同一に正極活物質を製造した。前記正極活物質の組成に対するＩＣＰ分析結果は、下記の表４に示した。

(4) Example 4
The positive electrode active material was produced in the same manner as in Example 1 except that 0.05 mol% of the Zr-containing compound (ZrO ₂ ) was additionally mixed with the synthesized precursor. The ICP analysis results for the composition of the positive electrode active material are shown in Table 4 below.

(5) Example 5
The lithium composite oxide is mixed with the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ), and after heat treatment, the Ti-containing compound (TIO ₂ ) 0. After additional mixing of 2 mol%, the positive electrode was the same as in Example 1 except that the temperature was raised to 400 ° C. at 2 ° C. per minute and heat-treated for 5 hours while maintaining the O ₂ atmosphere. Manufactured active material. The ICP analysis results for the composition of the positive electrode active material are shown in Table 5 below.

(6) Comparative Example 1
The lithium composite oxide is not mixed with the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ), and the temperature is raised to 400 ° C. at 2 ° C. per minute for 5 hours. The positive electrode active material was produced in the same manner as in Example 1 except that it was heat-treated. The ICP analysis results for the composition of the positive electrode active material are shown in Table 6 below.

(7) Comparative Example 2
A positive electrode active material was produced in the same manner as in Example 1 except that only the W-containing raw material (WO ₃ ) was mixed with the lithium composite oxide and then calcined. The ICP analysis results for the composition of the positive electrode active material are shown in Table 7 below.

(8) Comparative Example 3
A positive electrode active material was produced in the same manner as in Example 1 except that only the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) was mixed with the lithium composite oxide and then calcined. The ICP analysis results for the composition of the positive electrode active material are shown in Table 8 below.

(9) Comparative Example 4
The lithium composite oxide is not mixed with the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ), and the temperature is raised to 700 ° C. at 2 ° C. per minute for 5 hours. The positive electrode active material was produced in the same manner as in Example 1 except that it was heat-treated. The ICP analysis results for the composition of the positive electrode active material are shown in Table 9 below.

(10) Comparative Example 5
Same as in Example 1 except that after mixing only the W-containing raw material (WO ₃ ) with the lithium composite oxide, the temperature was raised to 700 ° C. at 2 ° C. per minute and heat-treated for 5 hours. A positive electrode active material was produced. The ICP analysis results for the composition of the positive electrode active material are shown in Table 10 below.

(11) Comparative Example 6
This was carried out except that after mixing only the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) with the lithium composite oxide, the temperature was raised to 700 ° C. at 2 ° C. per minute and heat-treated for 5 hours. The positive electrode active material was produced in the same manner as in Example 1. The ICP analysis results for the composition of the positive electrode active material are shown in Table 11 below.

(12) Comparative Example 7
After mixing the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ) with the lithium composite oxide, the temperature is raised to 700 ° C. at 2 ° C. per minute for 5 hours. The positive electrode active material was produced in the same manner as in Example 1 except that it was heat-treated. The ICP analysis results for the composition of the positive electrode active material are shown in Table 12 below.

Production example 2. Production of Lithium Secondary Battery 92 wt% of the positive electrode active material, 4 wt% of artificial graphite, and 4 wt% of PVDF binder produced in Production Example 1 were dispersed in 30 g of N-methyl-2pyrrolidone (NMP) to produce a positive electrode slurry. .. The positive electrode slurry was uniformly applied to an aluminum thin film having a thickness of 15 μm and vacuum dried at 135 ° C. to produce a positive electrode for a lithium secondary battery.

A lithium foil is used as a counter electrode with respect to the positive electrode, a porous polyethylene film (Celgard 2300, thickness: 25 μm) is used as a separation film, and ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3: 7. A coin cell was manufactured using an electrolytic solution in which LiPF ₆ was present at a concentration of 1.15 M in the solvent.

Experimental example 1. XRD analysis of the positive electrode active material X-ray diffraction (XRD) analysis was performed on the positive electrode active material produced in Production Example 1 to confirm the coating substance on the surface of the positive electrode active material _Nioc and the positive electrode active material. .. XRD analysis was performed using a Bruker D8 Advance diffraction meter (diffractometer) using Cu Kα radiation (1.540598 Å).

(1) _Niocc measurement of the positive electrode active material The occupancy rate (or content; Occupancy) was measured. The measurement results are shown in Table 13 below.

With reference to the results in Table 13, when a Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and a W-containing raw material (WO ₃ ) are mixed with the lithium composite oxide, Co is added to the lithium composite oxide. It can be confirmed that the occupancy rate of Ni inserted into the Li 3a site increases as compared with the case where only the contained raw material (Co ₃ (PO ₄ ) ₂ ) or the W-containing raw material (WO ₃ ) is mixed. .. Further, referring to Example 1 and Comparative Example 7, after mixing the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ) with the lithium composite oxide, the temperature is relatively low. By heat-treating at a temperature, the occupancy rate of Ni inserted into the Li 3a site can be improved.

In this way, the lithium composite oxide is mixed with the Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ), and then heat-treated at a relatively low temperature to cause the lithium. Co-containing raw material (Co ₃ (PO ₄ ) ₂ ) or W-containing raw material (WO ₃ ) alone is mixed with the composite oxide and then heat-treated, or Co-containing raw material (Co ₃ (PO ₄ ) 2) ₂ ) And the W-containing raw material (WO ₃ ) are mixed and then heat-treated at a relatively high temperature. It may be associated with the insertion of W into the Li 3a site by doping the tungsten in the crystal lattice of the substance.

(2) Analysis of Coating Substances in the Surface of Positive Substance Active Material Production Example 1 by a method of screening the oxides shown in Tables 14 and 15 below from XRD raw data measured using an EVA compound manufactured by Bruker. The content of the coating substance (ie, the second compound) in the surface of the positive electrode active material produced by the above was quantitatively analyzed.

The analysis results of the coating substance in the surface of the positive electrode active material analyzed by the above method are shown in Tables 14 and 15 below.

With reference to the results in Tables 14 and 15, unlike the positive electrode active materials according to Comparative Examples 6 and 7, in the case of the positive electrode active materials according to Examples 1 to 5, the lithium composite oxide was coated with Co. By mixing the contained raw material (Co ₃ (PO ₄ ) ₂ ) and the W-containing raw material (WO ₃ ) and then heat-treating at a relatively low temperature, in the oxide defined as the second compound in the present application, It was confirmed that the ratio of the compounds having a crystal structure (Co ₃ O ₄ , LiCo O ₂ and P ₂ O ₅ ) belonging to the space group Fd-3m, R3c or R-3m was 13 mol% or less.

On the other hand, in the case of the positive electrode active material according to Comparative Example 3, the positive electrode active material according to Example 1 was produced by the same method as the positive electrode active material except that the W-containing raw material (WO ₃ ) was heat-treated without mixing. It was confirmed that the oxides defined as the two compounds existed in a similar composition.

Experimental example 2. Measurement of unreacted lithium of positive electrode active material The measurement of unreacted lithium with respect to the positive electrode active material produced by Production Example 1 is measured by the amount of 0.1 M HCl used until pH 4 is reached by pH titration. did. First, 5 g of each of the positive electrode active materials produced in Production Example 1 was placed in 100 ml of DIW, stirred for 15 minutes, filtered, and 50 ml of the filtered solution was taken, and then 0.1 M HCl was added thereto. The amount of HCl consumed in response to changes in pH was measured to determine Q1 and Q2, through which the content of unreacted LiOH was calculated.

M1 = 23.95 (LiOH Molecular weight)
M2 = 73.89 (Li ₂ CO ₃ Molecular weight)
SPL Size = (Single weight x Solution Weight) / Water Weight
LiOH (wt%) = [(Q1-Q2) x C x M1 x 100] / (SPL Size x 1000)

The measurement results of the content of lithium impurities present in the positive electrode active material measured through the above formula are shown in Table 16 below.

(2) Evaluation of electrochemical characteristics of lithium secondary battery The lithium secondary battery manufactured by Production Example 2 is used in an electrochemical analyzer (Toyo, Toscat-3100) at 25 ° C. and a voltage range of 3.0 V to A charge / discharge experiment was carried out by applying a discharge rate of 4.3 V and 0.1 C to 5.0 C, and the initial charge capacity, the initial discharge capacity, the initial reversible efficiency and the discharge capacity ratio (C-rate) were measured.

Further, the lithium secondary battery manufactured by the above method is charged and discharged 50 times under the condition of 1C / 1C within the driving voltage range of 3.0V to 4.4V at a temperature of 25 ° C., and then the initial capacity is applied. The ratio of the discharge capacity to the 50th cycle (cycle capacity retention rate; capacity retention) was measured.

On the other hand, the initial resistance of the lithium secondary battery manufactured by Production Example 2 was measured within the frequency range (10 kHz to 0.01 Hz) using electrochemical impedance spectroscopy (EIS).

The measurement results are shown in Table 17 below.

Although the embodiments of the present invention have been described above, a person having ordinary knowledge in the art concerned can add, change, or delete components within the range not deviating from the idea of the present invention described in the claims. Alternatively, the present invention can be modified and changed in various ways by addition or the like, and it can be said that this is also included in the scope of the rights of the present invention.

Claims (11)

The first compound, which is capable of lithium intercalation / deintercalation,
A coating layer that is present on at least a part of the surface of the first compound and contains the second compound, and comprises.
The second compound is an oxide containing at least one first element selected from Group 1A elements, Group 3A elements and Group 5A elements, and at least one second element selected from Group 8 elements. Active material. The positive electrode active material according to claim 1, wherein the first compound is a lithium composite oxide having a layered crystal structure containing at least Ni and Co. The positive electrode active material according to claim 2, wherein the first compound is represented by the following chemical formula 1.
[Chemical formula 1]
Li _w Ni _{1- (x + y + z)} Co _x M1 _y M2 _z O _{2 + α}
(here,
M1 is at least one selected from Mn or Al, and is
M2 is at least one selected from Mn, P, Sr, Ba, B, Ti, Zr, Al, Hf, Ta, Mg, V, Zn, Si, Y, Sn, Ge, Nb, W and Cu. ,
M1 and M2 are different elements from each other,
0.5 ≦ w ≦ 1.5, 0 ≦ x ≦ 0.50, 0 ≦ y ≦ 0.20, 0 ≦ z ≦ 0.20, 0 ≦ α ≦ 0.02) The positive electrode active material according to claim 3, wherein x + y + z in the chemical formula 1 is 0.20 or less. The positive electrode active material according to claim 3, wherein the tungsten in the crystal lattice of the first compound is present. The positive electrode active material according to claim 1, wherein the second compound is represented by the following chemical formula 2.
[Chemical formula 2]
Li _a Co _b M3 _c (P _β O _γ ) _d
(here,
M3 is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ a ≦ 10, 0 ≦ b ≦ 8, 0 ≦ c ≦ 8, 0 <d ≦ 13, 0 <β ≦ 4, 0 <γ ≦ 10) The positive electrode active material according to claim 6, wherein the second compound contains a first oxide represented by the following chemical formula 3 and a second oxide represented by the following chemical formula 4.
[Chemical formula 3]
Li _{a'Co b'M3'c' ( P β'O γ'} ) _d'
(here,
M3'is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 <a'≤10, 0≤b'≤8, 0≤c'≤8, 0 <d'≤13, 0≤β'≤4, 0 <γ'≤10)
[Chemical formula 4]
Co _{b ″} M3 ″ _{c ″} (P _{β ″} O _{γ ″} ) _{d ″}
(here,
M3 ″ is Ni, Mn, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, W, Ce, At least one selected from V, Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ b ″ ≦ 8, 0 ≦ c ″ ≦ 8, 0 <d ″ ≦ 13, 0 ≦ β ″ ≦ 4, 0 <γ ″ ≦ 10) The positive electrode active material according to claim 1, further comprising a third compound represented by the following chemical formula 5 on at least a part of the surface of the first compound.
[Chemical formula 5]
Li _e W _f M4 _{g Oh}
(here,
M4 is Ni, Mn, Co, Fe, Cu, Nb, Mo, Ti, Al, Cr, Zr, Zn, Na, K, Ca, Mg, Pt, Au, B, P, Eu, Sm, Ce, V. , Ba, Ta, Sn, Hf, Ce, Gd and Nd.
0 ≦ e ≦ 10, 0 <f ≦ 8, 0 ≦ g ≦ 8, 2 ≦ h ≦ 13) The positive electrode active material according to claim 8, wherein the content of the second compound in the first compound is higher than the content of the third compound. A positive electrode containing the positive electrode active material according to any one of claims 1 to 9. A lithium secondary battery using the positive electrode according to claim 10.